The invention relates to polybenzimidazole articles and process for their production. More particularly, the invention relates to acid treated articles prepared from sintered polybenzimidazoles and a process for their production.
Polybenzimidazoles ar a known class of heterocyclic polymers which are characterized by a high degree of thermal and chemical stability. Processes for their production are disclosed in U.S. Pat. No. Re. 26,065, and U.S. Pat. Nos. 3,313,783; 3,509,108; 3,555,389; 3,433,772; 3,408,336; 3,549,603; 3,708,439; 4,154,919; and 4,312,976. All of the above-listed patents are incorporated herein by reference.
Aromatic polybenzimidazoles may be shaped to form fibers, films, and sintered articles of wide utility. The shaped products display great resistance to degradation by heat, hydrolytic media, and oxidizing media. Polybenzimidazole products have an ability to withstand continued exposure to elevated temperatures. The polymers may, for example, be dissolved in concentrated sulfuric acid and recovered without degradation by dilution with water.
Aromatic polybenzimidazoles are characterized by melt temperatures above about 400.degree. C., and, in many instances, by an ability to withstand temperatures in excess of about 500.degree. C. without softening or degrading. The polymer derived from isophthalic acid and 3,3'-diaminobenzidine is not melted by exposure to a temperature of 770.degree. C. and loses only 30% of its weight after exposure for several hours at temperatures up to 900.degree. C.
Further, although polybenzimidazole polymers are generally, more resistant to swelling by water than other types of polymers, such as cellulose acetate polymers, in a humid environment polybenzimidazole will absorb an appreciable amount of water. Hydrogen bonding at the site of the imidazole nitrogen-hydrogen bond with a water molecule will occur under humid conditions, thereby adversely affecting the performance of the polybenzimidazole polymer.
One method of reducing the hydrogen-bonding capability of the polybenzimidazole polymer is to replace the imidazole hydrogen with a hydrophobic species such as fluorine, phenol, trifluoromethyl and the like.
The present process seeks to reduce the ability of sintered polybenzimidazole products to absorb moisture from the environment. In situations where high dimensional stability is reguired, a non-swellable polybenzimidazole is desired. The present process comprises maintaining a liguid bath comprising water and a Lowry-Bronsted acid and immersing in the bath a polybenzimidazole substrate which was prepared from polybenzimidazole powder by a sintering process. The substrate is then removed from the acid bath, and dried in an inert atmosphere. Then the substrate is heat treated to obtain a final product. The final product is a sintered acid-treated polybenzimidazole substrate with has a substantially reduced capacity for absorbing moisture.
U.S. Pat. No. 4,927,909 (Wadhwa et al) discloses a process for the production of thermally stable polybenzimidazole films which comprises treating a sheet of polybenzimidazole with an agueous solution of phosphoric acid. This patent, however, fails to disclose a process for treating sintered polybenzimidazole substrates for the purpose of reducing moisture sorption capacity.
U.S. Pat. No. 4,460,708 (Stuetz) discloses a process for preparing activated carbon fibers comprising a step of treating a polybenzimidazole substrate with an acid solution. Phosphoric acid is disclosed as one of the possible acids useful in the invention. The '708 patent does not teach the preparation of a moisture resistant sintered polybenzimidazole substrate.
U.S. Pat. No. 4,628,067 (Chen, Sr. et al) discloses the treatment of polybenzimidazole resins with acidic solutions to prepare functionalized derivatives useful in the fields of catalysis and ion exchange resin preparation. The '067 patent fails to disclose acid treatment of sintered polybenzimidazole substrates to enhance moisture resistance characteristics.
Of particular interest in the preparation of useful polybenzimidazole shaped articles have been processes for preparing dimensionally stable substrates which can tolerate environments of high humidity. Here are numerous instances in which sintered polybenzimidazole parts are shaped to desired close dimensional tolerances, and will, if left untreated, change dimension on standing in uncontrolled humid atmospheres.
Accordingly, it is an object of the present invention to disclose a process for the preparation of sintered polybenzimidazole substrates having a substantially decreased capacity for sorbing moisture.
It is a further object of this invention to disclose a product prepared according to the process as outlined above.
These and other objects, as well as the scope, nature and utilization of the process and the products produced by that process will be apparent to those skilled in the art, from a review of the following detailed description and appended claims.